P. Lagrange

L'insertion dans le graphite des amalgames de potassium et de rubidium

Abstract Potassium and rubidium amalgams are able to intercalate into graphite and produce ternary compounds of two types. With amalgams rich in alkali metal, binary compounds with small amounts of mercury in the intercalated layers are obtained: MC 8 (Hg). With amalgams of composition around MHg, one can prepare ternary multilayered compounds named mercurographitides: in these compounds, the intercalated layers consist of two alkali metal planes with a sheet of mercury in between. The data for the first stage mercurographitides MHgC 4 are given in Table 2. The identity period along the c axis was obtained from X-rays data (Fig. 1, Table 1). The hk 0 reflexions show the octal epitaxy of the metal layers between the carbon planes (Fig. 2, Table 3). The intercalation of the amalgam occurs in two steps: first a quasiselective intercalation of the alkali metal (Fig. 3) and then a simultaneous intercalation of mercury and alkali metal (Fig. 4). The first step gives the compound MC 8 (Hg) and the second MHgC 4 . The second stage mercurographitides MHgC 8 are characterized by their identity period along the c axis (Fig. 5, Table 4) and are given in Table 5. A mechanism of addition of mercury to the MC 8 phases is proposed in Fig. 6. Finally, in an effort to prepare mercurographitides of stages higher than 2, the identity period along the c axis for the third stage compound was found, although this compound was not obtained in a pure state.

Insertion de metaux alcalino-terreux dans le graphite

Resume The pure first stage strontium and barium graphitides were prepared using two different methods: 1. (1) direct action of the metal vapor on the graphite, in metallic sealed tubes, 2. (2) compressing of the powders and heating of the mixture. From the physical properties of the alkaline Earth metals, it appears that the first method is favourable in most cases (Table 1). The formula MC 6 was clearly established from the chemical analysis (Table 3), weight uptake (Table 4) density (Table 5) and also from the planar unit cell (Fig. 2). The structure was obtained by a technique which allows to study separately the different families of reflexions: —001 from pyrolytic graphite (Table 6, Fig. 4); — hk 0 and Khl from single crystals. The relative intensities of the hk 0 and hkl reflexions (Table 7–9), and the systematic extinctions (Fig. 5) are in good agreement with the space group P 6 3 / mmc with two metal atoms in position b and twelve carbon atoms in i (Table 10, Fig. 3). The indexation of all reflexions in a powder X-ray diagram confirms this structure.

Insertion de lanthanoides dans le graphite

Abstract The intercalation of lanthanides is possible by two different ways: direct action of the metal vapor in metallic tubes sealed under vacuum or by heating compressed mixture of powders of the metal and of graphite. The first method was used only for the most volatile metals: samarium, europium, thulium and ytterbium (see Table 1). The 00 l reflexions of the corresponding first stage graphitides MC6 (M = Sm, Eu, Tm or Yb) were obtained for samples prepared from pyrolytic graphite HOPG (Tables 2 and 3, Fig. 1). Using the second method, we determined the identity period along the c axis (Ic) for the most fusible lanthanides graphitides (Table 4). We did a study of the evolution vs temperature of a compressed mixture of initial composition Yb + 6C (Fig. 2). A structural study was carried out on single crystals of europium and ytterbium graphitides, using a special method developed in the laboratory. Figure 3 shows the three possible types of sites available to the metal atoms and the different stacking modes of the metallic layers. The hkO and hkl reflexions of the graphitide YbC6 (see Table 5) shown in Fig. 5 allow to choose between the three possible unit cells of Fig. 4. The hexagonal unit cells of EuC6 and YbC6 belong to the space group P63/mmc with two of three sites occupied regularly by the metal atoms. The two metal atoms are in position b and the twelve carbon atoms in i. The parameters are respectively a = 4.314 ± 0.003 A , c = 9.745 ± 0.008 A (EuC 6 ) and a = 4.320 ± 0.004 A , c = 9.147 ± 0.004 A (YbC 6 ) .

The superoxide production mediated by the redox cycling of xenobiotics in rat brain microsomes is dependent on their reduction potential

Several exogenous molecules undergo enzymatic one-electron reduction leading to radicals which can rapidly react with molecular oxygen to form superoxide anions. We have previously shown that under aerobic conditions a significant superoxide anion production occurred during the NADPH-dependent one-electron reduction of some drugs and xenobiotics by rat brain preparations. We report here for several compounds a fairly good correlation between the reduction potentials (Epc vs. SCE) which ranged between - 230 and - 700 mV in aqueous medium (pH 7.4) or between -700 mV and -1100 mV in the aprotic solvent N,N-dimethylformamide, and the rate of superoxide anion production during their metabolism by rat brain microsomes. The data obtained suggest that the redox potential of most of the molecules assayed was related to their ability to undergo one-electron reduction mediated by flavoenzymes in the rat brain. The main range of reduction potentials corresponding to a large superoxide anion production suggests that the redox cycling of these chemicals was mediated by NADPH-cytochrome P-450 reductase. Therefore the measurement of reduction potentials of drugs and xenobiotics able to reach the brain, and chemically related to quinones, nitroaromatics, nitroheterocyclics and iminiums, may provide information both on their electron affinity and the possibility of one-electron transfer in vivo, and thus on their possible neurotoxicity due to the production of oxygenated free radicals.

Synthesis and electrical properties of some new ternary graphite intercalation compounds

Abstract New ternary graphite intercalation compounds (GICs) of general formula MBi x C 4n (M=K, Rb, Cs; x∼-0.6 ; n=stage) have been synthesized. The electrical resistivity, both parallel (π a ) and perpendicular (π c ) to the basal planes has been studied from 1.4 to 295 K. All in-plane behaviour is metallic ; the c axis conductivity is thermally activated except for the richest compounds. The cesium compounds are superconducting.

Superconductivity of graphite intercalated with thallium alloys

Abstract Superconductivity in the graphite intercalation compounds (GIC) KTl1.5C4 and KTl1.5C8 is reported with critical temperatures of Tc = 2.7 K and Tc = 2.45K respectively. The critical field behavior of the compound KTl1.5C4 was determined by a.c. susceptibility to be anisotropic ranging from 4 k0e parallel to ≅20 k0e perpendicular to the c -axis. KTl1.5C4 has the highest values of Tc and Hc2 observed to date in a graphite intercalation compound.

Intercalation of rare earth metals in graphite

Abstract Like lithium and alkaline-earth metals, some lanthanides are able to give intercalation compounds with graphite. The intercalation is obtained either by action on the graphite of the vapor of the metal or by compression and heating of mixtures of graphite and metal powders. The structure of the 1st stage compounds EuC 6 and YbC 6 was determined with oriented samples by separate study of the different families of reflections: 00 l with samples prepared from prolytic graphite, hk 0 and hkl with single crystals. The hexagonal unit cell of these 1st stage phases belongs to the space group P6 3 /mmc with two metal atoms in position b and 12 carbon atoms in i. The parameters are respectively, a = 4.314 ± 0.003 A, c = 9.745 ± 0.008 A (EuC 6 ) and a = 4.320 ± 0.004 A, c = 9.147 ± 0.004 A (YbC 6 ).

Superoxide anion production during monoelectronic reduction of xenobiotics by preparations of rat brain cortex, microvessels, and choroid plexus.

Brain microsomes may produce reactive metabolites during the reductive metabolism of some xenobiotics including drugs. These reactive species can, in turn, react with molecular oxygen to form superoxide radicals (O2.-). We measured the rates of superoxide production by homogenates obtained from three cerebral structures, cortex plus cerebellum, choroid plexus, and microvessels. The molecules assayed were related to quinone, nitroheterocycle, and iminium chemical families. The results we obtained showed a significant correlation between the rate of superoxide anion production and the apparent kinetic parameters (log Km/Vmax) of NADPH-cytochrome P450 reductase activity for these molecules, suggesting the involvement of this enzyme in xenobiotic-induced superoxide production.

Superconductivity of the graphite intercalation compounds KHgC8 and RbHgC8

Abstract Superconductivity was observed in the graphite intercalation compounds, KHgC 8 and RbHgC 8 , using an AC induction technique. The transition temperatures were 1.90K and 1.44K for KHgC 8 and RbHgC 8 respectively. A full Meissner effect was observed for KHgC 8 with a temperature dependant anisotropy in critical field with a value of 25 ± 5 at T c .

Graphite lamellar compounds EPR studies

We report X-band EPR results in a range of graphite lamellar compounds with: Li (stages I, II, III), K(I, II, III, IX), Rb (I, III) as donors and with: HNO3 (I), SO3(I, II, III) as acceptors. Line shapes are dysonian and g-anisotropy remains low even in stage IX K-compound. From line parameters, relaxation time T2 and c-axis electronic diffusion coefficient D are deduced. Results are discussed and compared with metal properties: T2 versus temperature, resistivity, stage and intercalant atomic number for donors, c-diffusion coefficient and mean free path, density of states estimations. Particularly KC8 is shown to exhibit more metallic properties than Li-compounds and low density of states are found in acceptors, contrary to donors, in agreement with 13C NMR.